Stroke and heart attack are the leading causes of mortality and grave morbidity. The goal of this Fast-Track STTR grant application is to enable preclinical investigation of WE-thrombin, a bioengineered protein C activator enzyme for the treatment of severe, acute thrombotic diseases, in particular ischemic stroke. WE- thrombin is a fundamentally new "thrombosis-specific" agent that may act in part by increasing the surface concentration of endogenous activated protein C (APC), which is an anticoagulant, profibrinolytic, and cytoprotective enzyme. Unlike any other antithrombotic drug, WE-thrombin is virtually inactive in the center of the blood stream or in static wound blood. WE-thrombin is a well-defined and far-advanced drug candidate, with antithrombotic efficacy and hemostatic safety verified in definitive primate studies. The proposed research will generate information for an Investigational New Drug (IND) application for WE- thrombin. Existing antithrombotic and thrombolytic drugs, such as recombinant tissue plasminogen activator (TPA) cause bleeding and, thus, cannot be used at their fully effective doses. In addition, TPA needs to be administered within the first 3 hours following onset of ischemic stroke. Since only a small percentage of stroke patients qualify for treatment in this narrow time frame, TPA is seldom administered. Thus, relevant to the mission of NIH, there is an urgent need for better drugs for stroke and other acute thrombotic diseases. The project addresses this need directly with WE-thrombin, which has shown outcome benefits compared to TPA in treating experimental acute ischemic stroke in preliminary studies using mice. Phase I has been designed to create pharmaceutically acceptable formulations of WE- thrombin that can be administered beyond the 3-hour treatment window of TPA in stroke. The 3 specific aims of Phase I are to develop a stable, injectable formulation of WE-thrombin (Aim 1) and to determine its efficacy (Aim 2) and safety (Aim 3) in comparison to TPA when administered in mice with advanced experimental acute ischemic stroke (AIS). Demonstration of efficacy and safety of WE-thrombin in AIS is the milestone that will move WE-thrombin development into Phase II, during which pharmaceutical GMP- grade (good manufacturing practice) WE-thrombin will be obtained and evaluated in vitro (Aims 4 &5) and subsequently tested in IND-enabling studies to determine its dose-limiting toxicity and potential side effects (Aim 6). Successful completion of Phase II will be defined as a preclinical safety and efficacy data package - and sufficient amount of formulated drug that is suitable for clinical studies. After Phases I and II, an IND application will be submitted, and upon FDA approval, WE-thrombin will be taken into clinical development. PUBLIC HEALTH RELEVANCE: Blood clots that block blood flow can cause acute heart attack and stroke that both remain among the three leading causes of death and severe chronic disability in the U.S., in part due to limited safety of clot-preventing and clot-removing drugs. The relevance of the proposed project to public health is that it is intended to develop a therapeutic agent (product) for safely interrupting and/or removing blood clots in acute thrombotic diseases. The new recombinant therapeutic enzyme - WE-thrombin - is a first-of-its-kind thrombosis-specific drug candidate that has the potential to represent a breakthrough in antithrombotic therapy for ischemic stroke. WE- thrombin has already been shown to be effective in treating experimental blood clots (thrombosis) in large primates - it is now intended to offer a safe and effective alternative to existing drugs that all had failed to fundamentally improve the morbidity and mortality of stroke, primarily due to their bleeding side effects.